Add a very simple test program

Not quite a unit test, it looks more like an example
but still something.

src/vm.cpp

@@ -271,6 +271,10 @@ namespace wren {
 		return nullptr != m_local->user_data;
 	}
 
+	std::size_t VM::dynafunc_byte_size() const {
+		return m_local->dynafunc.total_memory();
+	}
+
 	void VM::ensure_slots (int num_slots) {
 		wrenEnsureSlots(m_local->wvm, num_slots);
 	}